The inkjet printing industry has shown a significant growth in recent years. Marked improvements in inks and the performance of inkjet printers have been made and it is beginning to be possible for people to easily produce high-gloss, high-resolution images comparable to silver halide photographs at home.
As for inks in particular, rapid improvements have been made to enhance the image quality and reduce environmental impact, such as transition from conventional dye inks to pigment inks and transition from solvent-based inks to aqueous inks. Presently, aqueous pigment inks are actively being developed.
With improvements in the performance of inkjet printers and the like, it is required that inks have various properties. Examples of such properties include ink discharge stability in which clogging of ink discharging nozzles of inkjet printers over time is prevented and ink discharge failures and discharging of ink in inadequate directions are prevented in the long term, and blend stability in which separation or aggregation of inks containing a binder resin, a pigment or a dye, and other additives over time does not occur.
An example of inkjet printing inks with high ink dischargeability and blend stability is an ink composition that contains at least a pigment, water, water-insoluble vinyl polymer particles that contain the pigment and enable the pigment to disperse in the ink composition, and a urethane resin. This ink composition can be mixed with an acetylene glycol serving as a surfactant and used (e.g., refer to PTL 1).
However this ink composition falls short of the levels of dischargeability and blend stabilities required by the industry and sometimes causes clogging of ink discharge nozzles over time when used over a long term.